package chapter2;

import java.security.Security;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

import org.bouncycastle.jce.provider.BouncyCastleProvider;

/**
 * CBC using DES with an IV based on a nonce. In this case a hypothetical
 * message number.
 */
public class NonceIvCBCExample {
	public static void main(String[] args) throws Exception {
		Security.addProvider(new BouncyCastleProvider());
		byte[] input = new byte[] { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d,
				0x0e, 0x0f, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07 };
		byte[] keyBytes = new byte[] { 0x01, 0x23, 0x45, 0x67, (byte) 0x89, (byte) 0xab, (byte) 0xcd, (byte) 0xef };
		byte[] msgNumber = new byte[] { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };

		IvParameterSpec zeroIv = new IvParameterSpec(new byte[8]);

		SecretKeySpec key = new SecretKeySpec(keyBytes, "DES");

		Cipher cipher = Cipher.getInstance("DES/CBC/PKCS7Padding", "BC");

		System.out.println("input : " + Utils.toHex(input));

		// encryption pass

		// generate IV

		cipher.init(Cipher.ENCRYPT_MODE, key, zeroIv);

		IvParameterSpec encryptionIv = new IvParameterSpec(cipher.doFinal(msgNumber), 0, 8);

		// encrypt message

		cipher.init(Cipher.ENCRYPT_MODE, key, encryptionIv);

		byte[] cipherText = new byte[cipher.getOutputSize(input.length)];

		int ctLength = cipher.update(input, 0, input.length, cipherText, 0);

		ctLength += cipher.doFinal(cipherText, ctLength);

		System.out.println("cipher: " + Utils.toHex(cipherText, ctLength) + " bytes: " + ctLength);

		// decryption pass

		// generate IV

		cipher.init(Cipher.ENCRYPT_MODE, key, zeroIv);

		IvParameterSpec decryptionIv = new IvParameterSpec(cipher.doFinal(msgNumber), 0, 8);

		// decrypt message

		cipher.init(Cipher.DECRYPT_MODE, key, decryptionIv);

		byte[] plainText = new byte[cipher.getOutputSize(ctLength)];

		int ptLength = cipher.update(cipherText, 0, ctLength, plainText, 0);

		ptLength += cipher.doFinal(plainText, ptLength);

		System.out.println("plain : " + Utils.toHex(plainText, ptLength) + " bytes: " + ptLength);
	}
}
